Glucocorticoids, in topical, oral and inhaled formulations, are useful for their anti-inflammatory and immunosuppressive activities. Notwithstanding the sophistication of many formulations, many glucocorticoids exhibit significant side-effects that prevent realization of their maximum pharmacologic value. These side-effects stem, in part, from the difficulty of effectively delivering the glucocorticoid drug to a target tissue without increasing systemic concentrations of the drug.
Inhaled glucocorticoids are an effective therapy for the control of asthma, and improvement with steroids is one of the hallmarks of asthma [Barnes, P J (1998) in Asthma: Basic Mechanisms and Clinical Management (3rd ed)]. The inhaled glucocorticoids work to reduce the inflammation in either lungs, e.g. for asthma, or nose, e.g. for nasal allergies. Inhaled glucocorticoids are most often administered using a metered dose inhaler (MDI). In the best of circumstances, in controlled clinical settings, only around 30% of the administered dose gets into the lungs. In the general patient population probably only 10% or so of the dose gets into the lungs due to improper use of the inhaler. The rest of the administered drug is deposited in the throat and upper airways, or is swallowed. The drug that is deposited in the throat is responsible for some side effects seen with inhaled glucocorticoids (cough, oropharyngeal candidiasis and dysphonia). For early generation inhaled glucocorticoids, the swallowed drug leads to the same side effects seen with oral glucocorticoids. In light of the tremendous efficacy of inhaled glucocorticoids in asthma, much effort has gone into reducing the side effects from their use. Although newer glucocorticoids (e.g. budesonide, ciclesonide, triamcinolone and fluticasone) exhibit reduced systemic side effects from swallowed drug—being either poorly absorbed in the gut or subject to extensive inactivation in the liver—they nonetheless display systemic side effects as a result of absorption from the lung into the systemic circulation. The side effects include decreased bone density (Israel, E et al., (2001), New England Journal of Medicine 345:941-947 and Wong, C A et al., (2000) Lancet 355:1399-1403), which has been correlated with increased risk of fracture. Thus the need still exists for inhaled glucocorticoids with reduced systemic effects.
Several approaches have been suggested to reduce systemic effects. One such approach takes advantage of inactive prodrugs that are activated in the lung tissues. For example, Dietzel et al. [Prog. Respir Res. 31, 91-93 (2001)] have described an isopropyl group esterified at the 21 position of the glucocorticoid core structure. Another approach that has been suggested is the formulation of a glucocorticoid as a liposome. Axelsson et al. in a series of U.S. patents (U.S. Pat. Nos. 4,693,999; 5,614,514 and 5,888,995) describe selected glucocorticoids modified for formulation into liposomes by esterification at the 21 position with saturated and mono-unsaturated fatty acids with chain lengths up to 20 carbons.